1. Field of the Invention
This invention relates generally to semiconductor circuits and, more particularly, to a semiconductor circuit that can be used to activate an array of components coupled to the etch paths of a circuit board.
2. Description of the Related Art
As the speed at which data processing systems operate has increased, physical effects have become significant that previouisly could be ignored. Specifically, the distributed impedances of the printed circuit board etch paths, that could be ignored when circuit components were operated at lower frequencies, have now become important. These distributed impedances cause the circuit board etch paths to exhibit behavior analogous to the behavior of a transmission line at the increased operating frequencies. As a result, the control of the signal overshoot and undershoot (or ringing) with respect to the power supply potential and the ground (common) potential must be accomplished. For example, when memory array elements are coupled to the circuit board etch paths, the importance of controlling the signal overshoot and undershoot is the result of the strict tolerances specified by the manufacturer for the memory array elements. The ringing of the control signals can be understood in terms of transmission line theory wherein the overshoot and undershoot are the result of reflections when the transmission line is improperly terminated. When the rise and fall time of the applied control signals are less than the time for a reflected signal to return to the point of signal application, then the effects of the distributed impedance of the printed circut can not be ignored. The time T for an applied signal to be reflected and return to the point of application is given by: EQU T=2*L*(L.sub.o *C.sub.o).sup.1/2* (1+C.sub.L /C.sub.o).sup.1/2
where:
C.sub.L is the load capacitance per unit length along a transmission of length L, PA1 C.sub.o is the capacitance per unit length of the printed circuit board conducting paths, PA1 L is the length of the printed circuit board conducting paths, and PA1 L.sub.o is the inductance per unit length of the printed circuit board conducting path.
While the compensation for the signal ringing has been accomplished in the related art, the compensating techniques have not kept pace with the memory element array technology, a technology that has provided a doubling of the memory element density every two or three years.
A need has therefore been felt for a circuit that can control the rise and fall times of signals applied to the printed circuit boards (e.g. with memory array components), and that can be implemented in a technology compatible with the technology used in fabricating the memory array elements.